Method of manufacturing boards of vegetable material



P 1954 A. J. A. AsPLuNb 3,149,929

METHOD OF MANUFACTURINGBOARDS 0F VEGETABLE MATERIAL Filed April 14, 1959 Fig.1

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United States Patent Office 3,149,929 Patented Sept. 22, 1964 3,149,929 METHOD OF MANUFACTURING BOARDS OF VEGETABLE MATERIAL Arne Johan Arthur Asplund, 11 Orevagen, Bromma, Sweden Filed Apr. 14, 1959, Ser. No. 806,296 Claims priority, application Sweden Apr. 18, 1958 2 Claims. (Cl. 3416.5)

My present invention relates to a method to manufacture products composed of particles of a vegetable material cemented together in a hot press by means of a thermo-setting binder or glue.

More particularly my invention relates to a method to manufacture board-shaped products or slabs composed of particles of a vegetable material connected together in a hot press by means of a thermo-setting binder or glue.

Still more particularly my invention relates to a method to manufacture board-shaped products or slabs composed of a vegetable material cemented together in a hot press by means of a thermo-setting hinder or glue usually added to the particles in the form of an emulsion.

A typical example of products of the kind in consideration is constituted by chip boards in which connection the term chips is understood to define particles of wood or other vegetable material which may have a length of the order of 1 centimetre and a substantially minor thickness and breadth. In the following specification the application of my invention to the manufacture of such wood chip boards will be described though my invention is not limited thereto.

Prior to the addition of the binder the wood chip material is dried to a moisture content of about 8 to by weight. The drying ought not be too extensive because the chips otherwise become brittle and difficult to form. On the other hand, the partial drying is of importance since otherwise the curing of the binder will be unsatisfactory. To this pre-dried chip material an aqueous emulsion of the thermo-setting binder such as a synthetic resin glue is added, resulting in that the moisture content of the chip material is increased to between and Usually said moisture content is about 18%. The quantity of synthetic resin amounts to 4 to 8% and occasionally more depending on the varying properties of the chip material and the final use intended for the product.

The pre-formed boards of said composition are introduced into the hot press where they are exposed to pressure and the binder caused to cure so that a coherent board is obtained.

As will be easily understood from the aforesaid the finally compressed board has a considerable excess of moisture which in most cases must be removed before the board can be used for its intended purpose. The moisture content of an air-dry board thus should normally amount to the order of 8 to 10% only. Further the temperature of the chip material in the hot press has been increased considerably over normal room temperature, namely to between 80 and 140 C., normally between 85 and just over 100 C. and in most cases about 90 C.

The chip boards in order to remove their excess of moisture and simultaneously to cool them are stored after having left the press. Said storing is generally effected by stacking one board upon the other with interposed spacers permitting passage of air. In some cases this process is accelerated by forcing the air by means of fans or like apparatus to circuate between and over the boards. This storing in stacks with spacers is relatively time wasting and requires a large space. If the spacers are not placed with great exactness in line one above the other the boards are exposed to deformations which easily remain permanent since the boards after the hot pressing are relatively plastic. Of course the boards may be ground plane subsequently, but this operation is complicated especially when large deformations require much material to be removed. At the same time the boards treated in this manner will show undesired variations in thickness.

One main object of my invention is to eliminate the drawbacks inherent in the methods hitherto known by making use of the quantity of heat contained by the products or boards immediately after the treatment in the hot press to remove the excess of moisture. I have found that the boards when subjected to a treatment in vacuum will have their moisture content reduced to about the normal value and simultaneously their temperature to about room temperature.

In an experiment made by me I measured a chip board upon removal from a hot press to have a temperature of C. and a moisture content of 18%. I exposed said board to a vacuum which after 15 minutes reached an absolute pressure of about 20 mm. mercury column. The temperature dropped to 20 C. and the moisture content was reduced from 18% to 9.4% calculated per unit weight of dry material.

Since the residual heat content of the board provides for the required evaporation heat, the process according to my invention becomes very simple, it being thus not necessary to supply external heat for carrying out the process. As a consequence it becomes possible with advantage to stack a plurality of boards one upon the other and to provide the vacuum chamber with a resilient wall so as to expose the boards simultaneously to a mechanical pressure corresponding to the magnitude of the vacuum. Due to the fact that the drying and the cooling of the boards are effected under pressure any deformation of the boards is counteracted and the finished product is of a uniformly high quality.

Further objects and advantages of my invention will become apparent from the following description considered in connection with the accompanying drawing, which forms part of this specification and of which:

FIG. 1 is a longitudinal vertical sectional View through an apparatus for carrying out the method according tomy invention and FIG; 2 is a partial view of said apparatus in the same section but in an enlarged scale.

Referring to the drawing, reference numeral 10 denotes a supporting table and reference numeral 12 a preferably rectangular frame which is adapted to be lifted and lowered relatively to said table. In the embodiment shown diagrammatically in the drawing, wires 14, 16 are attached to said frame and pass over pulleys 18, 20, 22 and are connected to the piston 24 of a servomotor and movable within a cylinder 26 of said servomotor, which cylinder is rigidly secured to a base. A pressure fluid may be supplied to one or the other side of the piston through conduits 28, 30. In this way the frame 12 may be lifted from or lowered unto the supporting table 10.

When the frame 12 is in its lifted position a stack of chip boards 32 is introduced laterally which stack should just have left the above-mentioned hot press, not shown in the drawing, and which boards thus may be assumed to have a moisture content of about 18% and a temperature of 90 C. Attached to the lower edge of the frame is a resilient flange 34 which extends around said edge and is secured to the frame by means of strips 36 and screws 38. The resilient flange 34 is made of rubber, synthetic plastic or other similar material adapted to establish a sealing connection with the table 10. The top face of the frame is sealed by a resilient plate or membrane 40 made of synthetic plastic material, for example, which is rigidly secured about the upper edge border of the frame by means of strips 42 and screws 44, for example. Adjacent the frame the membrane 40 is reinforced by a flange 46 made also of resilient material.

Mounted on the inner wall of the frame is a system or coil of perforated tubes 48, which through a flexible hose 50 is connected to two vacuum pumps not shown. Spacers 52 may be provided between the tube coils.

After the frame 12 has been lowered to the table 10, the vacuum device is put into operation. In this connection it is suitable to remove as a first step a large quantity of air per unit time in order to obtain quick connection and sealing between the resilient flange 34 and the supporting table 10. This is effected by means of one of the two vacuum pumps which lowers the pressure to to 30 mm. mercury below the atmospheric pressure, for example, or if desired lower. Thereupon the evacuation is continued to below 100 to 50 mm. mercury absolute pressure. The vapor pressure of water having a temperature of 20 C. lies at about 20 mm. mercury. If this temperature is desired to be reached during the drying and cooling operation, the pressure must be reduced below said limit.

The stack of boards 32 has such height that the upper resilient membrane 40 will bear against the topmost board of the stack. Due to the evacuation and evaporation of excess moisture present inside the boards is caused and the heat required for this evaporation is taken from the boards themselves so that these boards are cooled to about room temperature. At the same time a uniform pressure acts on the uppermost board which pressure uniformly propagates through the stack to the lowermost board resting on the even topface of the table 10. When the boards are introduced into the evacuation chamber they have due to their increased temperature and large moisture content some plasticity which disappears through the treatment under vacuum. The form of the boards is thus stabilized while they are subjected to pressure.

The vegetable or lignocellulose containing material may even consist of woodlike constituents of flax stalks or like raw material. Although the products in the first instance are intended to be constituted by plane boards or slabs of uniform thickness intended for production of furniture, Walls, doors, shutters or the like finished products, they may even have bent or curved form or varying thickness. In the latter case the increased pressure created during the evacuation may be made use of to give the products or boards the desired shape. The hinder or glue used may be of the urea-formaldehyde resin glue type.

While one more or less specific embodiment of my invention has been shown and described, it is to be understood that this is for purpose of illustration only and that my invention is not to be limited thereby, but its scope is to be determined by the appended claims.

What I claim is:

1. The method of treating boards composed of particles of vegetable material united in a hot press by means of a thermo-setting, water-containing adhesive causing the boards to obtain a moisture and heat content in excess of that existant in boards that have been dried in atmosphere, the boards containing such excess moisture and heat being transferred to and stacked within a chamber provided with a movable wall overlying a face of the stack and while the boards have retained the elevated temperature received in the hot press, and exhausting the air from the chamber to thereby cause the movable wall of the chamber to be urged by outside atmospheric pressure against the face of the stack, the residual heat in the boards providing the latent heat of vaporization to remove the moisture from the boards.

2. The method according to claim 1 in which the air is exhausted from the chamber in two steps whereby the amount of air removed per unit of time is greater in the first step than in the second step while the air pressure decrease in the chamber is greater in the second step.

References Cited in the file of this patent UNITED STATES PATENTS 465,975 Howard Dec. 29, 1891 1,608,147 Vierling Nov. 23, 1926 1,763,070 Shinn June 10, 1930 2,387,595 Luth et al Oct. 23, 1945 2,661,543 Tyndall et al Dec. 8, 1953 2,886,101 Overton May 12, 1959 

1. THE METHOD OF TREATING BOARDS COMPOSED OF PARTICLES OF VEGETABLE MATERIAL UNITED IN A HOT PRESS BY MEANS OF A THERMO-SETTING, WATER-CONTAINING ADHESIVE CAUSING THE BOARDS TO OBTAIN A MOISTURE AND HEAT CONTENT IN EXCESS OF THAT EXISTANT IN BOARDS THAT HAVE BEEN DRIED IN ATOMSPHERE, THE BOARD CONTAINING SUCH EXCESS MOISTURE AND HEAT BEING TRANSFERRED TO AND STACKED WITHIN A CHAMBER PROVIDED WITH A MOVABLE WALL OVERLYING A FACE OF THE STACK AND WHILE THE BOARDS HAVE RETAINED THE ELEVATED TEMPERATURE RECEIVED IN THE HOT PRESS, ND EXHAUSTING THE AIR FROM THE CHAMBER TO THEREBY CAUSE THE MOVABLE WALL OF THE CHAMBER TO BE URGED BY OUTSIDE ATMOSPHERIC PRESSURE AGAINST THE FACE OF THE STACK, THE RESIDUAL HEAT IN THE BOARDS PROVIDING THE LATENT HEAT OF VAPORIZATION TO REMOVE THE MOISTURE FROM THE BOARDS. 